Four O'Clocks are bushy plants with many trumpet-shaped flowers that tend to open in the afternoon, or earlier on shady days. The flowers also emit a light delicate perfume. While common varieties come in red, pink, yellow or white, commercial seeds may come in mottled or multicolored varieties.
Four O'Clock seeds are black, surprisingly large, and thick-shelled. The seeds won't germinate unless they are well wetted. Unless you plant them in the rainy season, your best best is to fill a saucer with water and let the seeds soak up water overnight. After soaking the seeds may swell up a bit, but they should still be firm enough to plant easily.
If you want to start them indoors, then after soaking, put them in about 1/4" of soil. They should sprout quickly. They will grow towards the sun; you may want to turn them from day to day to keep them from growing at an angle. They also tend to grow a long deep root, so you shouldn't keep too many of them in one pot for too long!
If there's no danger of frost, the germinated seeds or little plants can be placed outdoors. Four O'Clocks prefer a sunny area, but can do well in partial shade. They can manage well in poor soil. If planted about a foot apart, each plant will grow into a bushy form with thick stalks, and hundreds of flowers.
In late summer and fall, the plant will form most of its seeds. These will hang onto the plant for some time, but will eventually dry and fall off. Thus, seeds can be collected by picking, or by shaking the plant, or simply by collecting the seeds that have already fallen. The Four O'Clock also grows a large tuber. If the winter is mild, the plant will grow back from this tuber the next year. Otherwise, the tuber may be dug up and stored in the garage or shed in a dark, moist environment, for replanting in spring.